Electric toilet problems

[prv]

Yes, but it only makes sense to work in the system in use where you live. There’s no point me calculating that I need a cable in Number 27 American Nonsense Units when UK suppliers only offer them in standard mm² sizes.

You seem to be doing all your sums in AWG, which implies that either Australian electrical suppliers stock AWG (or B&S), or you’ve never actually bought any wire and just spend all your time on Google, finding mostly US websites. I know you’ve built a boat, so I have to assume it’s the former. I’m just surprised that Australia doesn’t use the standard metric sizes.

Pete

 

[coopec]

Yes, but it only makes sense to work in the system in use where you live. There’s no point me calculating that I need a cable in Number 27 American Nonsense Units when UK suppliers only offer them in standard mm² sizes.

You seem to be doing all your sums in AWG, which implies that either Australian electrical suppliers stock AWG (or B&S), or you’ve never actually bought any wire and just spend all your time on Google, finding mostly US websites. I know you’ve built a boat, so I have to assume it’s the former. I’m just surprised that Australia doesn’t use the standard metric sizes.

Pete

Whatever......

 

[VicS]

I'm sure it will help but according to the table (above) you are still going too light.

For your 18A macerator and 20 feet you should be using 8ga (3.2mm diam/8.35mm² )

All these tables in various wire gauges are all very well but it is very simple arithmetic to calculate the volts drop if you know the length, cross sectional area and current

Copper has an electrical resistivity of 1.724 x 10^-8 Ω m ( this is the figure on which the tables are based and is well documented in the literature.)

Volts drop = Resistivity x length x current /area

If the length is 6m, the area is 6mm² , (or 6 x 10^-6m² ), and the current is 18amps
this works out as 0.31 volts
This is just inside the commonly applied figure of 3% ( for a 12 volt circuit)

6mm² will therefore be OK but 8.5mm² will be better ......... the volts drop with 8.5mm² will be 0.22volts at 18amps

No wire gauges or tables needed and not a Google in sight.

 

[coopec]

All these tables in various wire gauges are all very well but it is very simple arithmetic to calculate the volts drop if you know the length, cross sectional area and current

Copper has an electrical resistivity of 1.724 x 10^-8 Ω m ( this is the figure on which the tables are based and is well documented in the literature.)

Volts drop = Resistivity x length x current /area

If the length is 6m, the area is 6mm² , (or 6 x 10^-6m² ), and the current is 18amps
this works out as 0.31 volts
This is just inside the commonly applied figure of 3% ( for a 12 volt circuit)

6mm² will therefore be OK but 8.5mm² will be better ......... the volts drop with 8.5mm² will be 0.22volts at 18amps

No wire gauges or tables needed and not a Google in sight.

"Copper has an electrical resistivity of 1.724 x 10-8 Ω m"
Geez! I suppose any idiot would know that!?

I'll stick to google and online tables thanks! (I have no intention of becoming an electronics NERD)

But thanks anyway: you have confirmed my view that 8.5mm² is the way to go

NOTE:
When you say:
"this works out as 0.31 volts. This is just inside the commonly applied figure of 3%"
I am now confused. Did you mean outside the commonly.... ?

 

[VicS]

When you say:
"this works out as 0.31 volts. This is just inside the commonly applied figure of 3%"
I am now confused. Did you mean outside the commonly.... ?

No.
3% of 12volts is 0.36volts
The figure I calculated (0.31volts ) is just within this limit.

 

[PaulRainbow]

"Copper has an electrical resistivity of 1.724 x 10-8 Ω m"
Geez! I suppose any idiot would know that!?

No, they would not. But only an idiot would use such calculations to determine the correct wire size for an electric toilet on a boat. In the same way that one would have to be pretty stupid to work with AWG cable sizes in the UK, where the cable is sold in mm sq

I'll stick to google and online tables thanks! (I have no intention of becoming an electronics NERD)

But thanks anyway: you have confirmed my view that 8.5mm² is the way to go

Yes, stick to Google, it is what you do best (next to starting arguments on internet forums)

NOTE:
When you say:
"this works out as 0.31 volts. This is just inside the commonly applied figure of 3%"
I am now confused. Did you mean outside the commonly.... ?

6mm cable is under 3% voltage drop and is perfectly suitable for an electric toilet rated at 18A max.

By the way, why do you need to make your posts in a variety of fonts, sizes, colours and styles ? It doesn't make your posts any easier to read, it just looks like we are reading something written by a 6 year old who has just discovered crayons.

 

[PaulRainbow]

No.
3% of 12volts is 0.36volts
The figure I calculated (0.31volts ) is just within this limit.

If you are driving at 48MPH in a 50 MPH speed limit you are within the limit, there is no need to drive at 38MPH.

1.5mm cable carries more than enough current for an 18A load, but we go bigger to combat the voltage drop. 6mm cable is the acceptable size. Using 8.5mm the voltage drop is 0.01V less, how do you figure that is "better"? Why not go to 10mm, will that be "better"?

 

[coopec]

No, they would not. But only an idiot would use such calculations to determine the correct wire size for an electric toilet on a boat. In the same way that one would have to be pretty stupid to work with AWG cable sizes in the UK, where the cable is sold in mm sq

I buy my electrical cable from international sellers on eBay who can use AWG, B&S, mm (diam) and mm² to describe their product. I have no trouble determining which cable I need.

 

[PaulRainbow]

I buy my electrical cable from international sellers on eBay who can use AWG, B&S, mm (diam) and mm² to describe their product. I have no trouble determining which cable I need.

You are not in the UK, are you ?

If you were, you would, as i said, be stupid to work out all of your cable requirements in AWG when the cables are sold in mm²

 

[colind3782]

It was probably my fault for mentioning that the pump motor tails were marked as 14 AWG!

I ran the 6mm cable through but the existing pump still wouldn't run, probably seized a bit from me running it dry trying to test it. The new pump works fine but isn't an exact match so some jiggerypokery required to make a new base.

I did wonder why the pump tails are only 2.5mm and the control switch tails are tiny. Hopefully, upgrading the wiring has cured that problem but I might just order a spare pump anyway!

 

[PaulRainbow]

It was probably my fault for mentioning that the pump motor tails were marked as 14 AWG!

Not at all, it's the fault of those who only come here to argue ?

I ran the 6mm cable through but the existing pump still wouldn't run, probably seized a bit from me running it dry trying to test it. The new pump works fine but isn't an exact match so some jiggerypokery required to make a new base.

I did wonder why the pump tails are only 2.5mm and the control switch tails are tiny. Hopefully, upgrading the wiring has cured that problem but I might just order a spare pump anyway!

The pump tails are only 2.5mm because 2.5mm cable is rated at 30A, which is more than enough for the pump. It isn't, however, enough to counter the voltage drop, so we use fat cable to get close to the toilet with an acceptable voltage drop, then short 2.5mm cable tails are perfectly OK.

 

[claymore]

Been reading this with interest as we have an electric bog. which, touchwood, is reliable.
I'm not an electrician and don't have a technical or enquiring mind but it seems to my logic at least, that if the thing runs fine all season and then doesn't when it left for a while, it surely isn't really a wiring gauge issue?
If it was it would dither and faff each time intermittently
I think its more to do with the way it is left - or it might be an issue of diet - have you tried going vegetarian?

 

[colind3782]

Been reading this with interest as we have an electric bog. which, touchwood, is reliable.
I'm not an electrician and don't have a technical or enquiring mind but it seems to my logic at least, that if the thing runs fine all season and then doesn't when it left for a while, it surely isn't really a wiring gauge issue?
If it was it would dither and faff each time intermittently
I think its more to do with the way it is left - or it might be an issue of diet - have you tried going vegetarian?

Nothing solid goes through it, except in an emergency!, as we have excellent marina facilities for that kind of work . When we leave we flush through with fresh water then pour some vinegar and flush that enough so it sits in the outlet hose. All as recommended in these forums.

 

[coopec]

No, they would not. But only an idiot would use such calculations to determine the correct wire size for an electric toilet on a boat. In the same way that one would have to be pretty stupid to work with AWG cable sizes in the UK, where the cable is sold in mm sq

I'm surprised you say you don't use AWG cable sizes in the UK.

Yesterday I did a google search at random and came up with this UK Website where near 50% of cables were described in AWG terms as well as mm² .

https://uk.farnell.com/c/cable-wire-cable-assemblies/multicore-cable

 

[PaulRainbow]

I'm surprised you say you don't use AWG cable sizes in the UK.

Yesterday I did a google search at random and came up with this UK Website where near 50% of cables were described in AWG terms as well as mm² .

https://uk.farnell.com/c/cable-wire-cable-assemblies/multicore-cable

The UK is metric. I only use quality metric cable, connectors and tooling. The connectors are designed for the cable and the tooling likewise.

We also use metric fasteners as standard.

That doesn't mean that imperial nuts, bolts, spanners etc are not available. But one would have to be a special kind of idiot to buy imperial spanners to work with metric fasteners, in the same way, one would not work in AWG and then have to convert to mm when working with cables in a country where the standard cable system is metric.

 

[claymore]

I'm still not convinced this is a wiring issue - if it works when in regular use and then conks when its given a rest, why should that be a wiring issue?

 

[lustyd]

UK suppliers only offer them in standard mm2 sizes

I'm with you in spirit, but recent shopping experience shows that AWG is surprisingly common in the UK. Solar cables in particular seem to be AWG if you buy pre-made ones as they seem to be made for the US market. I think as Amazon takes over more and more distribution this will get worse rather than better. Proper electic suppliers all seem to use metric, but retailers don't seem to care.

For my boat I bought a red and back 6mm reel of tinned cable as I figured it's small enough not to be daft for most things and thick enough to cope with most loads without excessive volt drop. It also means standardised connectors like Wago of which I'm now a convert. I've yet to find anything away from the battery compartment, windlass and engine that need bigger. It probably cost more, but what I spent in extra copper I make up for in lower wastage.

 

[coopec]

I'm with you in spirit, but recent shopping experience shows that AWG is surprisingly common in the UK. Solar cables in particular seem to be AWG if you buy pre-made ones as they seem to be made for the US market. I think as Amazon takes over more and more distribution this will get worse rather than better. Proper electic suppliers all seem to use metric, but retailers don't seem to care.

For my boat I bought a red and back 6mm reel of tinned cable as I figured it's small enough not to be daft for most things and thick enough to cope with most loads without excessive volt drop. It also means standardised connectors like Wago of which I'm now a convert. I've yet to find anything away from the battery compartment, windlass and engine that need bigger. It probably cost more, but what I spent in extra copper I make up for in lower wastage.

It might be a while since PRV and Paul bought electrical cable?
With the Internet sellers are supplying buyers all around the world so measurements can't afford to be parochial.

I don't see it as a problem. While building the boat I had to convert.

US gallons to gallons
Tonnes to tons.
Pounds to KG
Centigrade to fahrenheit
Inches to cm
Feet to meters
AWG to mm²
pounds to kilopascals...........

 

[PaulRainbow]

I'm with you in spirit, but recent shopping experience shows that AWG is surprisingly common in the UK. Solar cables in particular seem to be AWG if you buy pre-made ones as they seem to be made for the US market. I think as Amazon takes over more and more distribution this will get worse rather than better. Proper electic suppliers all seem to use metric, but retailers don't seem to care.

For my boat I bought a red and back 6mm reel of tinned cable as I figured it's small enough not to be daft for most things and thick enough to cope with most loads without excessive volt drop. It also means standardised connectors like Wago of which I'm now a convert. I've yet to find anything away from the battery compartment, windlass and engine that need bigger. It probably cost more, but what I spent in extra copper I make up for in lower wastage.

The most common size of wire on a boat is 2.5mm, followed by 1.5mm. I also use some 4mm, 6mm, 8mm, 10mm and of course, various sizes of battery cable.

Basic rule of thumb for me is, if 1.5mm is suitable, use it (i generally don't use anything less for power cables, other than maybe some N2K power connections). If it needs more then 1.5mm, i use 2.5mm, if suitable. If 2.5mm is not big enough i then use whichever of those other sizes are correct. There are few things that need more than 2.5mm, toilets, fridges, certain pumps, cables to shared distribution boards being a few, plus the obvious like windlasses, bow thrusters etc.

 

[PaulRainbow]

It might be a while since PRV and Paul bought electrical cable?
With the Internet sellers are supplying buyers all around the world so measurements can't afford to be parochial.

Seriously ?

What do you imagine i use to wire the boats up with, that i do every day of my working life ?

I do not and will not buy AWG cable. All of my connectors and tools are designed for metric cable.

I also do not use imperial nuts on metric bolt and vice versa